A treadmill comprises a bottom frame and a deck for a user to stand thereon. The deck is provided with an endless treadmill belt to circle round the deck. Because the treadmill belt of the treadmill is tightly matched with two transmission rollers, under the long-term friction between the deck and the treadmill belt, the treadmill belt is likely to cause a crack to affect its service life. The joint way of the treadmill belt of a conventional treadmill is that both ends of the treadmill belt have a certain length to be overlapped and connected by hot pressing to form an endless treadmill belt. The contact area of the joint of both ends of the treadmill belt is small. Under the long-term friction between the deck and the treadmill belt, the joint of both ends of the treadmill belt is easy to break to affect its service life. In view of this, the inventor of the present invention have carefully studied and developed a more practical joint structure, allowing the endless treadmill belt to be more stable. The present invention has been developed after many attempts of conceiving and testing.